Biostratigraphy, Microfacies and Depositional Environment of the Sarvak Formation at the Pyun Anticline (Zagros Basin, Southwest of Iran)

Abstract

AbstractThe Sarvak Formation is a carbonate sequence of Late Albian–Early Turonian age in Zagros Basin in Iran. In this investigation, the Sarvak Formation at the Pyun Anticline section (Izeh Zone) has been studied. It consists of 797 m thick limestone which overlies the Kazhdumi Formation conformably and underlies the Gurpi Formation unconformably at the Pyun Anticline. A very rich fossil association (85 genera and 132 species) characterizes the Pyun section. Based on the stratigraphic distribution of diagnosed foraminifera, five biozones are established: 1, Muricohedbergella‐Globigerinelloides sp. assemblage zone (Late Albian); 2, Praealveolina iberica‐Chrysalidina gradata interval zone (Early Cenomanian); 3, Chrysalidina gradata‐Cisalveolina fraasi (fallax) and C. lehneri interval zone (Middle Cenomanian); 4, C. fraasi (fallax) and C. lehneri‐Praetaberina bingistani assemblage zone (Late Cenomanian); 5, Nezzazatinella picardi‐Mangashtia‐Dicyclina assemblage zone (Early Turonian). Based on the petrographic and sedimentological analyses, some 13 carbonate microfacies were identified. The investigated microfacies confirm a ramp‐type paleoenvironment. These microfacies, from distal to proximal environments, consist of: MF1: planktonic foraminifera wackestone‐packstone; MF2: Oligostegina planktonic foraminifera wackestone to packstone; MF3: planktonic‐benthic foraminifers sponge spicules wackestone‐packstone; MF4: rudist floatstone; MF5: rudist rudstone; MF6: bioclast intraclast grainstone; MF7: peloid intraclast grainstone; MF8: benthic foraminifers rudist grainstone‐packstone; MF9: peloid bioclast grainstone‐packstone; MF10: bioclast (benthic foraminifers) wackestone‐packstone; MF11: peloid bioclast packstone; MF12: dacycladacea benthic foraminifera packstone‐wackestone; MF13: miliolids wackestone‐packstone.